Electrodynamic Response Properties

Research Subject

Our research focuses on the description of materials properties based on direct results from quantum field theory and relativistic electrodynamics in media. More specifically, we investigate the behaviour and relations between so called "response functions" which contain the information on how a system behaves under external perturbations. A good example for such a response function is the (relative) permittivity εr, also known as the dielectric constant (e.g. εr,H2O = 88, εr,vac = 1), which relates the external electric field Eext to the induced electric field Eind. Sometimes instead of a constant, the permittivity is shown as a function of the frequency εr → εr(ω). However, this is still not the general expression. In fact, all response functions in real space are non-local integral kernels and additionally not simple scalar functions but entire 2nd rank tensors (3x3 matrices) and transform in Fourier space to tensors depending on a wave vector k and a frequency ω, i.e. εr εr(k,ω).

Even for the simple model of the free electron gas, this form leads to non-trivial complications in analytic calculations. Likewise, we encounter severe difficulties on the numercial/computational side, since response calculations take extraordinary amounts of computational time and memory and thus are still hard to perform even on state-of-the-art high-performance-cluster hardware.

With this research, we are looking forward to find a better and ideally even computationally more efficient way to calculate response functions like the dielectric tensor, the (optical) conductivity and even the refractive index, all based on ab initio Density Functional Theory (DFT) ground state calculations.

For more information on quantum field theory of materials, please visit our website https://qftmaterials.wordpress.com. There you can find an extended list of our publications on this topic as well as on the functional renormalization and mean-field approach to multiband systems with spin-orbit coupling.

Tools & Software

  • Pen, Paper & Brain
  • ELK (FP-LAPW DFT code)
  • Elk Optics Analyzer (optics data post-processing tool)
  • Quantum Espresso (pseudo potential DFT code)
  • GPAW (pseudo potential DFT code)
  • ASE (atomic simulation environment)
  • lots of self-written scripts and tools


Dr. Ronald Starke2591OG. 25Ronald [dot] Starkeatphysik [dot] tu-freiberg [dot] de
René Wirnata2591OG. 25Rene [dot] Wirnataatphysik [dot] tu-freiberg [dot] de
Prof. J. Kortus4008OG. 16Jens [dot] Kortusatphysik [dot] tu-freiberg [dot] de

Collaboration Partners

  • Institut für Theoretische Festkörperphysik, RWTH Aachen
    (Dr. Giulio A.H. Schober)
  • Semiconductor Physics Research Group, TU Chemnitz
    (Prof. Dr. Georgeta Salvan)
  • Institut für Elektrotechnik, TU Freiberg
    (Matthias Saurbier, Prof. Jana Kertzscher)


Articles in international journals & preprints

  • Wavevector-dependent optical properties from wavevector-independent proper conductivity tensor
    R, Starke, G.A.H. Schober, R. Wirnata, N. Bulut, J. Kortus (accepted Nov. 2019)
  • Microscopic theory of refractive index applied to metamaterials
    R. Starke, G.A.H. Schober: arXiv preprint (September 2017)
  • Microscopic theory of the refractive index
    R. Starke, G.A.H. Schober: Optik. 140 (Juli 2017)
  • Linear electromagnetic wave equations in bulk materials
    R. Starke, G.A.H. Schober: Photonic.Nanostruc. (Sept. 2017)
  • Why history matters: ab initio rederivation of Fresnel equations confirms microscopic theory of refractive index
    R. Starke, G.A.H. Schober: arXiv preprint (Mai 2017)
  • General form of the full electromagnetic Green function in materials physics
    G.A.H. Schober, R. Starke: arXiv preprint (April 2017)
  • Covariant Response Theory and the Boost Transform of the Dielectric Tensor
    R. Starke, G.A.H. Schober: arXiv preprint (Februar 2017)
  • Ab initio electronic structure and optical conductivity of bismuth tellurohalides
    S. Schwalbe, R. Wirnata, R. Starke, GAH Schober, J. Kortus,
    Phys.Rev.B. 94 (20) (November 2016)
  • Relativistic covariance of Ohm's law
    R. Starke, G.A.H. Schober: Int.J.Mod.Phys.D, 25 (11) (Okt. 2016)
  • Ab initio materials physics and microscopic electrodynamics of media
    R. Starke, G.A.H. Schober: arXiv preprint (Juni 2016)
  • Response Theory of the Electron-Phonon Coupling
    R. Starke, G.A.H. Schober: arXiv preprint (Mai 2016)
  • Functional approach to electrodynamics of media
    R. Starke, G.A.H. Schober: Photonic.Nanostruc. 14 (April 2015)


  • Microscopic Theory of the Refractive Index
    R. Starke, G.A.H. Schober
    Verhandlungen DPG (2016), HL 36.21 (Poster)
  • Theoretical investigation of BiTeX (X=Cl,Br,I): Crystal structure and optical conductivity
    R. Wirnata, S.Schwalbe, G. Schober, J. Kortus, R. Starke
    Verhandlungen DPG (2016), MM 15.15 (Poster)
  • Ab initio expression of magneto-electric coupling coefficients in terms of current response function
    R. Starke, G.A.H. Schober
    Verhandlungen DPG (2015), DF 5.29 (Poster)
  • Functional Approach to Electrodynamics of Media
    R. Starke, G.A.H. Schober
    Verhandlungen DPG (2015), MA 19.15 (Poster)
  • Functional Approach to Electrodynamics of Media
    R. Starke, G.A.H. Schober
    Verhandlungen DPG (2014), MA 19.33 (Poster)

Graduate Theses / Dissertations

  • Master Thesis, René Wirnata (Okt. 2016)
    Supervisor: J. Kortus, R. Starke
    DOI: 10.13140/RG.2.2.32474.34243